How long can you use charcoal in the fish tank?

Charcoal, or activated carbon, can typically be used in a fish tank for about 4 to 6 weeks before it becomes saturated with impurities and loses its effectiveness. After this period, it should be replaced to maintain optimal water quality. It's important to rinse the charcoal before use to remove any dust and avoid introducing particulates into the tank. Regular monitoring of water parameters can help determine the best replacement schedule.